The present invention relates to object display technology in three-dimensional images.
Conventionally, a technique is known that an object arranged in a world coordinate system is perspective transformed to a screen coordinate system. In the conventional technique, the object arranged in the world coordinate system is transformed to a viewpoint coordinate system in which the coordinates of a viewpoint in the world coordinate system are an origin point and the direction of a line of sight is a z-axis. Then, the object transformed to the viewpoint coordinate system is projected onto the screen coordinate system which is a plane vertical to the z-axis in the viewpoint coordinate system relative to the origin point of the viewpoint coordinate system.
In the conventional technique, each object has multiple vertex coordinates defined in a unique local coordinate system that is defined by three-dimensional coordinates. The origin point of a local coordinate system corresponding to each object is arranged at the coordinates in the world coordinate system where each object is to be arranged, and thus each of the vertex coordinates defined in the local coordinate system of each object is associated with the coordinates in the world coordinate system. Therefore, each object is arranged in the world coordinate system.
Subsequently, each of the vertex coordinates of each object in the world coordinate system is individually transformed to the viewpoint coordinate system, and then each object is transformed from the world coordinate system to the viewpoint coordinate system. Furthermore, each of the vertex coordinates of each object in the viewpoint coordinate system is projected onto the screen coordinate system relative to the origin point of the viewpoint coordinate system, and thus each object in the viewpoint coordinate system is perspective transformed to the screen coordinate system.
In this manner, each object in the viewpoint coordinate system is perspective transformed to the screen coordinate system relative to the origin point of the viewpoint coordinate system. Therefore, an object at a long distance from the viewpoint coordinate is projected onto the screen coordinate system small, whereas an object at a short distance from the viewpoint coordinate is projected onto the screen coordinate system large. Accordingly, how each object in the world coordinate system is seen from the viewpoint coordinate in the world coordinate system can be truly reproducted so as to match with the real world.